This research project has the following objectives: 1. To define the cytopathologic mechanism of hyperbaric oxygen toxicity in neurons in terms of structural and ultrastructural events, 2. To determine and interrelate the associated pathophysiologic changes and biochemical correlates with the structural abnormalities, 3. To determine and interrelate the same parameters of observations on hyperbaric oxygen toxicity in other cells: heart, skeletal muscle, liver, spleen, kidney and testes. The principal methods to be employed in carrying out the objectives of this study are: 1. Electron microscopy, 2. Ultrastructural cytochemistry, 3. Light microscopy, 4. Polarographic measurement of oxygen tensions under hyperbaric oxygen conditions with simultaneous physiologic monitoring (EEG, EKG, blood pressure, respiration, and body temperature), 5. Direct visualization of microcirculation under hyperbaric oxygen using fiber optic light guides and image conductors, 6. Differential ultracentrifugation in density gradients, gel electrophoresis, and spectrophotometry, as applied to various models of hyperbaric oxygen exposure of infant and adult animals.